The dipole moment of chlorobenzene is lower than that of cyclohexyl chloride mainly because of the structural and electronic differences between the two molecules:

• In chlorobenzene, the carbon attached to chlorine is sp2 hybridized (part of an aromatic benzene ring), while in cyclohexyl chloride, the carbon is sp3 hybridized. The sp2 carbon in chlorobenzene is more electronegative than the sp3 carbon, reducing the electronegativity difference between carbon and chlorine in chlorobenzene and thus lowering the bond polarity.
• The C-Cl bond in chlorobenzene has partial double bond character due to resonance with the aromatic ring. This partial double bond character shortens the bond length compared to the single bond in cyclohexyl chloride.
• Since dipole moment is the product of charge separation and bond length, the shorter C-Cl bond length and the lower electronegativity difference in chlorobenzene reduce its dipole moment.
• Additionally, resonance and electron delocalization in chlorobenzene distribute electron density, which also diminishes the net dipole moment compared to cyclohexyl chloride, where the dipole moment mainly arises from the straightforward polar C-Cl single bond.

In summary, the combination of a shorter bond length, reduced polarity due to sp2 carbon electronegativity, and resonance effects in chlorobenzene results in a lower dipole moment than in cyclohexyl chloride.